Re: Live migration leaves page tables read-only?

[John Byrne <john.l.byrne@hp.com>]

John Byrne wrote:
> Ian Pratt wrote:
>>> I forgot to mention that a very simple test case I wrote using shared
>>> memory and the mprotect call didn't fail. So, the only test case I
>> have
>>> at the moment is to run SAP.
>>
>> What happens if you use non-live relo?
> 
> I thought I had tested that way back at the beginning without seeing the 
> problem, but I must not have, because I just retested it to be sure and 
> it died the same way. (Now I am truly confused and I need to go back and 
> re-examine some of my earlier experiments.)
> 

After redoing some of my tests and understanding more about how Xen 
handles page tables, I started looking at ptwr_do_page_fault() and put 
debugging code into it. (On Xen 3.0.3 x86-64.)  The fixup is failing in 
x86_emulate_memop(). Building a debug version of Xen provided some 
additional information (the final line is from my debugging, after the 
":" is domid, addr, pte, pte flags, type_info, page owner, domain):


(XEN) DOM1: (file=mm.c, line=1682) Bad type (saw 0000000028000001 != exp 
00000000e0000000) for mfn c8de3 (pfn 12491)
(XEN) DOM1: (file=mm.c, line=606) Error getting mfn c8de3 (pfn 12491) 
from L1 entry 00000000c8de3167 for dom1
(XEN) DOM1: (file=mm.c, line=1682) Bad type (saw 0000000028000001 != exp 
00000000e0000000) for mfn c8de3 (pfn 12491)
(XEN) DOM1: (file=mm.c, line=606) Error getting mfn c8de3 (pfn 12491) 
from L1 entry 00000000c8de3067 for dom1
(XEN) DOM1: (file=mm.c, line=3120) ptwr_emulate: could not 
get_page_from_l1e()
(XEN) ptwr_do_page_fault,3253:1 ffff880011065bc0 80100000ca20f065 801065 
28000001 ffff830000fe7080 ffff830000fe7080

I'll keep following this down, but any help would be appreciated.

Thanks,

John Byrne